1. Field of the Invention
In general, the present invention relates to systems and methods that are used to steam reform liquid fuel to generate a volume of mixed gases. More particularly, the present invention is related to systems and methods that extract hydrogen from a combined mixture of fuel and water that undergoes a water gas shift reaction.
2. Prior Art Description
In industry, there are many applications for the use of ultra pure molecular hydrogen. For instance, there are many fuel cells that operate using hydrogen. The hydrogen, however, must be ultra pure. In the art, ultra pure hydrogen is commonly considered to be hydrogen having purity levels of at least 99.999%. Any molecules of carbon dioxide, carbon monoxide or other contaminant gases that are received by the fuel cell either reduces its efficiency or causes damage to the fuel cell.
Hydrogen gas does not exist naturally on earth to any significant extent because it reacts with many elements and readily combines to form compounds. Hydrogen gas must therefore be manufactured. Hydrogen gas can be manufactured in a number of ways. For instance, hydrogen gas can be created by splitting water molecules through electrolysis. However, the power needed for electrolysis is always greater than the power available from a fuel cell that utilizes the output hydrogen gas from the electrolysis. Any fuel cell system that obtains hydrogen gas from electrolysis, therefore, results in a net power loss.
Techniques have been developed where hydrogen gas can be extracted from the reformate gases of a hydrocarbon fuel and water mixture that have undergone an endothermic reaction. This initial endothermic reaction occurs between 250° C. and 1000° C., wherein the hydrocarbon fuel and water are primarily converted into hydrogen (H2), carbon monoxide (CO), methane (CH4), carbon dioxide (CO2) and water (H2O). The amount of energy required for the reaction depends upon the hydrocarbon being used. A principle challenge is to efficiently supply the energy needed to exhaust the chemical reactions.
The useful chemical energy in the resultant gases is contained in the H2, CO and CH4. The chemical energy in these three resultant gases contains the chemical energy that was originally in the hydrocarbon fuel, plus some of the endothermic energy that was used to heat the reaction.
The resultant gases of H2, CH4, CO and CO2 are used in a water gas shift reaction. The resultant gases are mixed with steam at an elevated temperature of between 300° C. and 450° C. In this temperature range, a water gas shift reaction is induced. Once the water gas shift reaction is induced, the CO and the CH4 present in the resultant gases react with the water (H2O). The CO and the H2O react as follows:CO+H2O→CO2+H2 It can therefore be seen that a large amount of hydrogen gas can be created by the water gas shift reaction. The hydrogen gas is then purified by drawing the hydrogen gas through a hydrogen permeable membrane in a hydrogen separator. The efficiency of this process can be improved when the steam is first removed from the reformate gas stream prior to the separation of the hydrogen. This increases the partial pressure of the hydrogen in the reformate stream, thus making the hydrogen permeation through the membrane much more efficient. The purified hydrogen can then be used to power a fuel cell or serve some other industrial purpose. Systems that utilize a water gas shift reaction in such a manner are exemplified by U.S. patent application Ser. No. 11/341,541, now U.S. Pat. No. 7,704,485 entitled System And Method For Processing Fuel For Use By A Fuel Cell Using A Micro-Channel Catalytic Hydrogen Separator, and U.S. patent application Ser. No. 11/522,139, now abandoned, entitled System And Method For Efficiently Extracting Ultra-Pure Hydrogen Gas From A Hydrocarbon Fuel.
The equations of the water gas shift reaction provided above, of course, react until a chemical balance is achieved. In reality, very few chemical reactions continue until exhaustion. Accordingly, in reality, when a water gas shift reaction occurs, some methane, carbon monoxide, and water remains in the raffinate gas. The amount of carbon monoxide that remains depends largely upon the steam to carbon ratio present in the reaction. The present invention describes a steam reformer assembly and a fuel processor system that utilizes the steam reformer assembly to increase the efficiencies of the reforming reaction by readily and uniformly transferring the energy in the combustion chamber to the fuel and steam mixture. The present invention steam reformer and fuel processor system are described and claimed below.